science museum

Chromosomes and Down syndrome

People with Down syndrome have 47 chromosomes, rather than the usual 46. They have an extra copy of chromosome 21, the smallest chromosome. Scientists can use a technique called 'chromosome painting' to diagnosis this condition. It uses a special type of fluorescing probe, which lights up all the chromosome 21s.

Chromosome painting lights up the extra chromosome 21 in the cells of people with Down syndrome (pink and light blue dots).
Chromosome painting lights up the extra chromosome 21 in the cells of people with Down syndrome (pink and light blue dots).
Joyce Harper/Wellcome Photo Library

Science Museum Home Page Who am I? Science Museum Home Page